1. Field of the Invention
This invention relates to a method for correcting the results of biochemical analyses. This invention particularly relates to a method for correcting the results of biochemical analyses wherein errors in the analyses or a variation in values obtained from the analyses, which errors or variation are caused by a difference in characteristics between a plurality of groups of analysis media, are eliminated. Typical reasons for such errors or variation are a difference in characteristics between production lots of analysis media, and a difference in characteristics between groups (for example, packaging units) of analysis media, which have been stored for different periods. The biochemical analyses are carried out with analysis media containing a color forming reagent, which will chemically react with a specific biochemical substance contained in liquid samples, such as blood or urine,.and give rise to a change in optical density, or with analysis media containing an electrochemical sensor which will electrochemically react with the biochemical substance and give rise to a change in current or potential. In the biochemical analyses, the liquid samples are independently applied to the analysis media, and changes in optical density or changes in current or potential, which changes have occurred in the analysis media, are measured. Thereafter, a calibration curve, which represents the relationship between the changes in optical density, or the changes in current or potential, and the concentrations or the activities of the biochemical substance in the liquid samples, is used in order to determine the concentrations or the activities of the biochemical substance from the measured changes in optical density or the measured changes in current or potential. This invention also relates to a biochemical analysis apparatus for carrying out the method for correcting the results of biochemical analyses. This invention further relates to a correction value recording medium which is used to carry out the method for correcting the results of biochemical analyses and on which a correction value corresponding to the change in characteristics between groups of analysis media is recorded.
2. Description of the Prior Art
Qualitative or quantitative analyses of specific chemical constituents in liquid samples are conducted for various industrial purposes. Particularly, it is very important in biochemical and clinical fields to be able quantitatively to analyze certain chemical or physical constituents in body fluids such as blood or urine.
Recently, dry type chemical analysis slides and test films were developed for use in systems designed for performing quantitative analyses, with which systems the amounts of specific chemical constituents or specific physical constituents contained in droplets of liquid samples, which are applied to the chemical analysis slides or the test films, are determined. For example, film-shaped chemical analysis elements, which are to be used in colorimetry, and chemical analysis slides which accommodate them are disclosed in U.S. Pat. Nos. 3,992,158 and 4,292,272. A film-shaped immunoanalysis (or immunoassay) element, which is to be used in fluorometry or colorimetry, and an immunoanalysis slide which accommodates it are disclosed in European Patent No. 0,051,183A. An immunoanalysis slide which is to be used in fluorometry or colorimetry is disclosed in U.S. Pat. No. 4,587,102. Also, an electrolyte analysis slide comprising a pair of ion selective electrodes, which pair serves as an electrochemical sensor, is disclosed in U.S. Pat. No. 4,053,381. Additionally, electrolyte analysis slides for analyzing a plurality of constituents, each of which slides comprises several pairs of ion selective electrodes serving as electrochemical sensors, are disclosed in U.S. Pat. No. 4,437,970 and European Patent No. 0,212,612A.
It is possible to analyze liquid samples more simply and more quickly with methods in which analysis media such as chemical analysis slides and test films are used than with methods in which conventional wet type analyses are carried out. Therefore, it is more desirable to use chemical analysis slides, particularly in medical organizations, research laboratories, or the like, where many samples must be analyzed, than to carry out conventional wet type analyses.
In order to use an analysis medium, such as a chemical analysis slide or a test film, in the quantitative analysis of a chemical constituent or the like contained in a liquid sample, a droplet of the liquid sample is put on the analysis medium and is kept at a predetermined temperature (i.e. incubated) for a predetermined time in an incubator, which causes a color reaction. The analysis medium is then exposed to light having a wavelength which is selected in advance. The selection of the wavelength depends on the specific biochemical substances contained in the liquid sample and the constituents of a reagent contained in the analysis medium. Light is thus irradiated to the analysis medium, and the optical density is measured. The optical density depends on how much of a reaction product was formed by the reaction between the liquid sample and the reagent in the analysis medium. Thereafter, a calibration curve, which is created in advance and which represents the relationship between the optical densities and the concentrations of the specific biochemical substance in liquid samples, is used in order to determine the concentration of the biochemical substance in the liquid sample from the optical density which was measured.
In order to use a chemical analysis slide comprising at least one pair of ion selective electrodes, which serves as an electrochemical sensor, in the quantitative analysis of a biochemical constituent or the like contained in a liquid sample, a droplet of the liquid sample and a droplet of a reference liquid are respectively put on the ion selective electrodes and are kept at a predetermined temperature (i.e. incubated) for a predetermined time in an incubator, which causes a difference in potential to occur between the ion selective electrodes. The difference in potential is measured. Thereafter, a calibration curve, which is created in advance and which represents the relationship between the differences in potential and the concentrations (or the activities) of a specific biochemical substance in the liquid samples, is used in order to determine the concentration (or the activity) of the biochemical substance in the liquid sample from the measured difference in potential.
A biochemical analysis apparatus has also been proposed with which both the optical density and the current or the difference in potential occurring between at least one pair of ion selective electrodes can be measured.
Problems which occur with a typical example of an analysis conducted with the conventional technique will be described hereinbelow. For this analysis a colorimetric or fluorometric, biochemical analysis method and apparatus are used in order to measure the optical density of the analysis medium, which depends on how much of a reaction product was formed by the reaction between a liquid sample and a reagent in the analysis medium. The same problems also occur with a biochemical analysis method and apparatus wherein an analysis medium provided with an electrochemical sensor is used in order to measure the current or the difference in potential occurring across the electrochemical sensor.
In order to determine the concentration of a specific biochemical substance contained in a liquid sample with a biochemical analysis apparatus, it is necessary to create a calibration curve in advance, which represents the relationship between the optical densities and the concentrations of a specific biochemical substance in liquid samples. The optical densities are measured with an optical densitometer located in the biochemical analysis apparatus. In order to create the calibration curve, the concentrations of the specific biochemical substance in a plurality of liquid samples are measured with one of several methods which have heretofore been established and which are different from the method employed in the biochemical analysis apparatus. Thereafter, the biochemical analysis apparatus is used in order independently to apply the liquid samples to analysis media, such as chemical analysis slides or long test films, and to incubate the analysis media to which the liquid samples have been applied. The optical densities are then measured which depend on how much of a reaction product was formed in the reaction between the liquid samples and the reagent in the analysis media. The optical densities thus measured are plotted on a graph with respect to the corresponding concentrations of the specific biochemical substance in the liquid samples.
FIG. 8 is a graph showing an example of the calibration curve created in the manner described above. In FIG. 8, the optical densities measured with an optical densitometer located in the biochemical analysis apparatus are plotted on the vertical axis, and the concentrations of the specific biochemical substance in liquid samples are plotted on the horizontal axis. The curve indicated by the solid line represents a calibration curve created in the manner described above. Even when the concentration of the specific biochemical substance in a liquid sample is 0.0, the optical density of the analysis medium, such as a chemical analysis slide or a test film, is not equal to 0.0. This is because the background density, i.e. the optical density of the analysis medium with no liquid sample applied thereto, is not equal to 0.0.
However, it often occurs that the optical density, which is measured with an optical densitometer in the manner described above, cannot be directly converted into the concentration of a specific biochemical substance in the liquid sample in accordance with the calibration curve.
The aforesaid calibration curve was created with a biochemical analysis apparatus corrected for accuracy (hereinafter referred to as the "standard biochemical analysis apparatus") and standard analysis media. (A calibration curve created with a standard biochemical analysis apparatus and standard analysis media will hereinafter be referred to as a "standard calibration curve".) A standard calibration curve cannot be directly used to measure the concentration of a specific biochemical substance in a liquid sample. This is primarily because, even when the same liquid sample is applied to a plurality of analysis media, the optical densities of the analysis media will vary in accordance with their characteristics, which should be substantially the same but which differ. The characteristics between production lots of analysis media vary, and a difference in characteristics between groups (for example, packaging units) of analysis media which have been stored for different periods also exists. (Such differences in characteristics will hereinafter be referred to as the "difference in characteristics between a plurality of groups of analysis media".) When the analysis is not required to be highly accurate, the difference in characteristics between a plurality of groups of analysis media can be ignored. When a highly accurate analysis must be conducted, the value of the optical density measured from an analysis medium is corrected, for example, in the manner described below. It is also considered that the biochemical analysis apparatus, which is actually used to carry out analyses, will differ in characteristics from the standard biochemical analysis apparatus. (The biochemical analysis apparatus which is actually used to carry out analyses will hereinafter be referred to as the "object biochemical analysis apparatus".) However, the difference in characteristics between the object biochemical analysis apparatus and the standard biochemical analysis apparatus will not be taken into consideration hereinbelow. This is because, ordinarily, errors in analyses, which are caused by the difference in characteristics between the object biochemical analysis apparatus and the standard biochemical analysis apparatus, are markedly smaller than errors in analyses, which are caused by the difference in characteristics between a plurality of groups of analysis media. Additionally, the difference in characteristics between the object biochemical analysis apparatus and the standard biochemical analysis apparatus can be substantially eliminated if the object biochemical analysis apparatus is appropriately maintained periodically or daily.
In order for the values of the optical densities measured from analysis media to be corrected, three types of standard liquids containing the specific biochemical substance in low (L), middle (M), and high (H) concentrations are prepared. Thereafter, a standard biochemical analysis apparatus is used in order to apply the standard liquids to the standard analysis media. Optical densities are then measured from the standard analysis media. In this manner, as shown in FIG. 8, optical densities DL, DM, and DH are measured for the three types of standard liquids. Therefore, from the calibration curve (i.e. the standard calibration curve) indicated by the solid line in FIG. 8, the concentrations of the specific biochemical substance in the three types of standard liquids are measured as being CL, CM, and CH. It is only necessary for the standard liquids to be prepared so that they always contain their constituents in a stable state. The concentrations CL, CM, and CH measured in the manner described above need not necessarily be equal to the correct concentrations of the specific biochemical substance in the three types of standard liquids. Thereafter, the object biochemical analysis apparatus is used in order to apply the standard liquids to analysis media, which are actually to be used in order to analyze liquid samples, and to measure the optical densities from the analysis media. (The analysis media which are actually to be used in order to analyze liquid samples will hereinafter be referred to as the "object analysis media". Also, because the difference in characteristics between the object biochemical analysis apparatus and the standard biochemical analysis apparatus is ignored, the standard biochemical analysis apparatus may be used at this time.) In cases where optical densities DL', DM', and DH' are thus measured from the object analysis media, the standard calibration curve is corrected into the calibration curve indicated by the broken line in FIG. 8, with which calibration curve the optical densities DL', DM', and DH' are respectively converted into the concentrations CL, CM, and CH. (The calibration curve which has thus been corrected will hereinafter be referred to as the "corrected calibration curve".)
After the corrected calibration curve is created in the manner described above, information about the corrected calibration curve is recorded in association with the corresponding object analysis media. For example, the method described below is employed, which is equivalent to the creation of a corrected calibration curve. Specifically, the standard calibration curve is used in order to measure concentrations CL', CM', CH' of the specific biochemical substance, which correspond respectively to the optical densities DL', DM', and DH' measured from the object analysis media. Thereafter, the concentrations CL', CM', CH' are respectively substituted into the quadratic equation EQU C=c(C').sup.2 +d(C')+e (1)
wherein C' represents the concentration of the specific biochemical substance, the variation in which concentration has not been corrected for, and C represents the concentration of the specific biochemical substance, the variation in which concentration has been corrected for. In this manner, the coefficients c, d, and e are calculated. Information about the three coefficients is, for example, written on a sheet of paper, and the sheet of paper is packaged together with the object analysis media. Information about the standard calibration curve is stored in advance in the object biochemical analysis apparatus, in which object analysis media are used in order to measure concentrations of the specific biochemical substance in liquid samples. Before object analysis media are used in the object biochemical analysis apparatus, the information about the coefficients c, d, and e is entered into the object biochemical analysis apparatus. Thereafter, the object biochemical analysis apparatus applies a droplet of a liquid sample to an object analysis medium, and the concentration C' of the specific biochemical substance is measured, the variation in which concentration has not been corrected for. Equation (1) is then used in order to calculate the corrected value of the concentration C of the specific biochemical substance from the measured concentration C'. In this manner, the liquid sample can be analyzed accurately.
The technique for correcting the standard calibration curve in the manner described above is disclosed in, for example, European Patent No. 0,247,439A. This reference teaches that, when different calibration curves are required for different batches of test media (i.e. when the characteristics of the test media differ between groups of the test media), information about how the calibration curve should be corrected is indicated with a bar code for each package (or each container) of the same batch of test media. The bar code is recorded on the packaging material or on a film separate from the test media. However, with the disclosed technique, the calibration curve is corrected manually. Specifically, information which instructs how the calibration curve is to be corrected is manually entered from a keyboard of the analysis apparatus in accordance with the information recorded on the packaging material or the film.
In cases where the difference in characteristics between a plurality of groups of analysis media is small (but is so large that the calibration curve must be corrected), the method described below is employed. The method will hereinbelow be described with reference to FIG. 9: FIG. 9 is an explanatory graph showing a different method for correcting a calibration curve.
In FIG. 9, the horizontal axis of the graph represents concentrations C1 of the specific biochemical substance, which were measured with a conventional analysis system other than the biochemical analysis apparatus. The vertical axis represents concentrations C2 of the specific biochemical substance, which were measured with the biochemical analysis apparatus. The solid line represents the relationship between the concentrations C1 and the concentrations C2, which concentrations C2 were measured with the standard biochemical analysis apparatus and the standard analysis media. In cases where the standard calibration curve was created accurately, C2=C1, i.e. the solid line takes on the form of a straight line which passes through the origin of the graph and has a slope equal to 1.0. The broken line represents the relationship between the concentrations C1 and the concentrations C2, which concentrations C2 were measured with the object biochemical analysis apparatus and the object analysis media. (Because the difference in characteristics between the object biochemical analysis apparatus and the standard biochemical analysis apparatus is ignored, the standard biochemical analysis apparatus may be used in lieu of the object biochemical analysis apparatus.) Because the difference in characteristics is present between a plurality of groups of analysis media, the broken line takes on the form of a straight line expressed as EQU C2=p.multidot.C1+q (2)
In cases where the difference in characteristics between a plurality of groups of analysis media is small, instead of the information about the coefficients c, d, and e being recorded, information about the coefficients p and q is recorded in association with the corresponding object analysis media. When the object analysis media are used in the object biochemical analysis apparatus in order to analyze liquid samples, values obtained from the analyses are corrected with the coefficients p and q. In this manner, the liquid samples can be analyzed accurately.
Heretofore, an operator of the object biochemical analysis apparatus has had manually to input the information about the coefficients c, d, and e or the information about the coefficients p and q from a keyboard, or the like, into the object biochemical analysis apparatus. Therefore, a problem often occurs because incorrect information is entered by mistake into the object biochemical analysis apparatus, and incorrect results of analyses are obtained from the object biochemical analysis apparatus. Even when this problem occurs, it is not easy to recognize that the problem has occurred. Additionally, the manual input of the information is troublesome.
The method described below has been suggested for eliminating these problems. For example, a bar code, which represents the information about the coefficients c, d, and e or the information about the coefficients p and q, is recorded on each object analysis medium. Also, a bar code reader is located in the object biochemical analysis apparatus. After the analysis medium is put into the object biochemical analysis apparatus, the bar code is automatically read from the analysis medium by the bar code reader and entered into the object biochemical analysis apparatus.
In general, so that the analysis media can be produced efficiently, a sheet or a tape having a large area, from which a large number of analysis media are to be produced, is prepared and stored. When the analysis media are produced from the sheet or the tape, the sheet or the tape is slit and cut into a plurality of pieces. The pieces are then inserted into slide mounts (or slide frames) and subjected to processes such as aging. In this manner, the analysis media are completed. The single sheet or the single tape, from which a large number of analysis media are produced, constitutes a single production lot. If the production lot exhibited approximately uniform characteristics during the production process and little change in characteristics during storage, and if the processes, such as the aging, of the pieces cut from the sheet or the tape were carried out under exactly the same conditions, it would be possible to employ the method described below. Specifically, in order to allow the coefficients c, d, and e or the coefficients p and q to be determined, a small number of pieces are slit and cut from the sheet or the tape. The pieces are then inserted into mounts and subjected to processes such as aging. A small number of analysis media thus produced are then used in order to determine the coefficients c, d, and e or the coefficients p and q. Thereafter, the information about the coefficients c, d, and e or the information about the coefficients p and q is recorded on many mounts. The remaining part of the sheet or the tape is then slit and cut into pieces. The pieces thus obtained are inserted into the mounts, on which the information about the coefficients c, d, and e or the information about the coefficients p and q has been recorded. The pieces which have been inserted into the mounts are then subjected to processes such as aging. In this manner, it would be possible to produce the analysis media on which the information about the coefficients c, d, and e or the information about the coefficients p and q has been recorded.
However, actually, some types of analysis media have a high sensitivity, and their characteristics easily change due to ambient temperature and humidity, and due to solvents, or the like, which are contained in the ambient air. For analysis media having a high sensitivity, the problem described below occurs. Specifically, the coefficients c, d, and e or the coefficients p and q are determined for analysis media having a high sensitivity in the manner described above, and the information about the coefficients is recorded on the mounts. Thereafter, the pieces cut from the sheet or the tape, from which such analysis media are produced, are inserted into the mounts, and subjected to processes such as aging. In the course of such analysis media being produced, the characteristics thereof become different from the characteristics of the analysis media, which were used in order to determine the coefficients c, d, and e or the coefficients p and q. Such a difference in characteristics is caused by, for example, a small difference in the conditions, under which the sheet or the tape was stored, and particularly by a small difference in the conditions under which the pieces inserted into the mounts were aged. Also, a high cost and considerable labor are required to prepare in advance the mounts on which the information about the coefficients c, d, and e or the information about the coefficients p and q has been recorded.
In order to solve these problems, the method described below has been suggested. Specifically, mounts on which no information about the coefficients has been recorded are prepared. Pieces cut from the sheet or the tape are then inserted into the mounts and subjected to processes such as aging. Thereafter, the coefficients c, d, and e or the coefficients p and q are determined from the analysis media thus produced, and the information about the coefficients are printed on the mounts of the analysis media.
However, analysis media having a high sensitivity are easily affected by a solvent contained in the printing ink, and the solvent causes the characteristics of the analysis media to change.
A method wherein the information about the coefficients c, d, and e or the information about the coefficients p and q is printed on labels and the labels are adhered to the mounts of the analysis media might also be considered. However, with this method, there is the risk of the analysis media being adversely affected by the adhesive which is used to adhere the labels to the mounts.
As described above, information about the coefficients c, d, and e or information about the coefficients p and q is necessary in order to correct the results of biochemical analyses. Additionally, other information, such as the name of the biochemical substance which is to be analyzed with the analysis media, is necessary in order to specify the analysis media. On the other hand, the mounts of the analysis media are used primarily for the purpose of supporting the analysis media. When a bar code, or the like, is recorded on a mount, the area over which the bar code, or the like, can be recorded is limited, and the bar code, or the like, must be recorded accurately. Therefore, a limitation is imposed on the amount of the information (for example, the number of code digits representing the information) which can be recorded on the mount. For this reason, a problem occurs in that there is not enough space to record the information necessary for correcting the results of the biochemical analyses (such as the information about the coefficients c, d, and e or the information about the coefficients p and q). For example, when the information about the coefficients c, d, and e is to be recorded in order to cope with large differences in characteristics between production lots of the analysis media, it is necessary for the code to have 12 digits (i.e. 4 digits.times.3). Even when the differences between production lots of the analysis media are small and information about the coefficients p and q is to be recorded, it is necessary for the code to have, for example, 4 digits (i.e. 2 digits.times.2). It is difficult to record such a large amount of information on a mount, or the like, together with the other necessary information, such as the name of the biochemical substance.